"None of us are under any illusion that reinstating that ban would be easy," Obama said at a press conference after his meeting with Mexican President Felipe Calderon in Mexico City. "What we've focused on is how we can improve our enforcement under existing laws."

Calderon, who would like the assault weapons ban reinstated because he believes Mexico was safer before it expired, said that he understands that "this is a politically delicate topic" in the United States.

Despite the possibility Obama might abandon his promise to restore the assault weapons ban, Obama told Calderon he would push for Senate ratification of another weapons-related measure, the inter-American arms trafficking treaty, according to the White House. The treaty, aimed at curbing the trafficking of guns and ammunition regionally, was signed by former President Bill Clinton in 1997 but was never ratified in the Senate.

"The president felt that it was important to push now for the ratification of this treaty because the question of illegal small-arms is of great concern to the countries throughout the hemisphere at it affects their safety," a senior administration official told ABC News. "The president's belief that steps need to be taken conveys our commitment to address this challenge."

Obama and Calderon also announced they are establishing a partnership to address clean energy and climate change. An administration official said that this is just the "launch of a process" and noted that the cooperation can be seen as "overcoming the perception in a constructive way" that the two nations cannot see eye-to-eye on some energy issues.

While there is no new actual policy on the environment, only a framework, the White House pointed to the agreement as further evidence of the United States and Mexico's mutual responsibility for shared problems and desire to cooperate.

Obama to Push for Ratification of Arms Treaty

President Obama will push for Senate ratification of the inter-American arms trafficking treaty at a press conference with President Felipe Calderon in Mexico City later this afternoon.

White House officials confirmed that the announcement will be made following President Obama's meeting with the Mexican president.

"The president felt that it was important to push now for the ratification of this treaty because the question of illegal small arms is of great concern to the countries throughout the hemisphere at it affects their safety," a senior administration official told ABC News. "The president's belief that steps need to be taken conveys our commitment to address this challenge."

The treaty, aimed at curbing the trafficking of guns and ammunition regionally, was signed by former President Bill Clinton in 1997 but was never ratified in the Senate.

In the first visit by an American president to Mexico City in 12 years, President Obama faces hot-button issues such as trade, immigration and escalating violence that will further complicate his economic agenda at home.

Obama arrived in Mexico City Thursday afternoon to meet with President Calderon. Over the weekend, Obama travels to a summit of Latin American and Caribbean leaders on the island of Trinidad.

With almost 6,300 killings in Mexico last year, U.S. officials fear that violence will spill over the border. Obama has said he wants to reduce the demand for drugs coming into the United States and the flow of guns and money crossing the border in the other direction.

"A number of weapons going into Mexico are coming from the United States, so we have moved agents, resources, we actually have dogs that are trained to sniff guns. We have moved them to do southbound checks as well as continuing and enhancing the northbound work that we're doing," Homeland Security Secretary Janet Napolitano said on "Good Morning America."

On Wednesday, Napolitano named Alan Bersin, a former federal prosecutor, to a new post overseeing border security and illegal immigration issues. In that role Bersin will serve as Napolitano's senior advisor on these issues and work closely with Mexican officials.

In an interview with "Nightline's" Terry Moran, Calderon adamantly rejected the notion -- advanced in a Pentagon report in December and echoed by some Latin America watchers -- that Mexico is on the verge of become a "failed state." He said some of the blame for his country's violence should be aimed at the United States and the demand for drugs here.

Obama's visit to Mexico's teeming capital of 20-million plus people is the first by an American president in 12 years. When former president George W. Bush traveled to Mexico, he went to smaller cities and resort towns.

The White House says the visit to Mexico is meant to show support for Calderon, who Obama sat down with before his inauguration to talk economic and security issues.

"The stop in Mexico is meant to send a message, and that is it's a message of admiration for the courageous steps that President Calderón has undertaken," said Denis McDonough, director of strategic communications at the National Security Council. "It is meant to send a signal of respect, mutual respect with our Mexican neighbors."

Obama and Calderon are expected to talk about trade and economic issues and immigration, which, though usually such a hot-button issue in U.S.-Mexican relations, will likely take a back seat to the more urgent matters of the drug trade and security.

One potentially contentious issue relates to the revocation of a pilot program that allowed Mexican commercial trucks to enter the United States. Mexico fired back by slapping tariffs on nearly 90 U.S. products, up to $2.4 billion worth of export goods, and has threatened to raise them even more if the United States doesn't restore the program.

McDonough said the White House is working on a resolution with Congress and Mexico by which the United States would be in line with its obligations under NAFTA, but he would not say if there would be an announcement on this issue today.

Obama Likely to Be Most Popular Guy in the Room

This weekend Obama heads to the Summit of the Americas, a meeting of the 34 countries in the western hemisphere with democratically elected governments. The summit will take place in Port of Spain, the capital of Trinidad and Tobago.

The only country in the hemisphere that will not be represented is Cuba, which does not have a democratically elected government and is not a member of the Organization of American States.

Just as he was in Europe, Obama is likely to be the most popular guy in the room. Latin America experts say expectations are high because it is the first time most of these leaders will be meeting Obama and his presidency marks a turning point from the Bush years.

The White House has not announced which leaders Obama will meet with one-on-one.

The global economic crisis will be a big part of the summit agenda, but leaders will also discuss related issues such as expanding renewable energy, reducing global warming, security and trade.

Obama administration officials say the president will address his support for "bottom up" economic development that helps the "poorest of the poor."

But analysts say the trip is really more about the beginning of a dialogue on regional issues and they don't expect anything concrete to develop.

Obama Arrives in 'Listening Mode,' Without an Open Checkbook

Mauricio Cardenas, director of the Latin America Initiative at the Brookings Institution, noted that Obama is there in "listening mode" -- because he is not coming with an open checkbook.

"There are things that Latin American leaders want to hear from the president of the United States," Cardenas said, pointing to the message that Obama took with him to Turkey last week. "They want to hear that there is no war on governments to the left or to the right of the spectrum and so long as countries hold democratic elections, Obama will have good relationships with leaders regardless of their ideology."

Abraham Lowenthal, professor of international relations at the University of Southern California and the co-editor of "The Obama Administration and the Americas: Agenda for Change" said Obama has "tremendous" appeal in the western hemisphere, but the summit may not produce any specific agreements.

"The general approach and image of the United States will be significantly transformed by this encounter, so I think this is something that's well worth the effort being put into it," Lowenthal said.

Far-Left Leaders Could Put Pressure on Obama

The Obama Administration tackled one large looming issue before taking off for the trip -- easing some travel and business restrictions relating to Cuba.

On Monday the White House announced that it will allow unlimited visits to family members on the island as well as unlimited remittances -- the cash recent immigrants to the United States send to relatives back home. President Bush imposed stricter restrictions on both in 2004.

The Obama administration will also take steps to enhance the flow of information by allowing U.S. telecommunications networks to link the United States and Cuba, and will allow an expansion of humanitarian items that can be sent to the island (including clothing, personal hygiene items and fishing equipment).

It will remain illegal to send items to senior government officials and members of the Communist Party.

While many Latin American leaders applauded these steps, there will still be pressure on Obama from leaders ranging from Mexico's Calderon to Venezuela's Hugo Chavez to lift the U.S. embargo on Cuba, imposed by President John F. Kennedy six months after Obama was born.

Tensions were high at the last Summit of the Americas, in Argentina in 2005, and leaders pushed through two days of tough negotiations on trade issues only to come away with little accomplished.

Before the meetings began, Chavez revved up a crowd of 10,000 anti-Bush demonstrators at a rally at a soccer stadium near the summit site, slamming the administration's policies on trade and Cuba, among other issues.

Analysts say that while Chavez is likely to try and stir the pot again this year, his language toward Obama has been much cooler than that toward Bush and his inflammatory rhetoric will not have the same impact as it did in the past.

"Tensions will be lifted just because of what President Obama represents," Cardenas said. "It's not easy for someone like Chavez to portray Obama as imperialist and oppressive, two slogan words when referring to President Bush. Those just don't seem to fit President Obama, they don't seem correct."

White House Press Secretary Robert Gibbs said Wednesday that Obama will not avoid Chavez or other leaders who have been critical of the United States, but he did not say if Obama would sit down one-on-one with the Venezuelan president.

"If we didn't sit in the same room with people that were critical of this country, we'd probably be sitting in a room all alone. We certainly wouldn't have gone to Europe," Gibbs said. "But the fact that some people have critical things to say, it hasn't and won't deter the president of the United States from looking for areas of common interests."